Scaling is the process of numerically measuring a health state utility. Utility is a global, composite, preference-based measure of health-related quality of life. Utility-based measures ask respondents to indicate their preference or desire for a health state, either their own or a hypothetical description. Utilities are scaled from 0 (death) to 1 (full or perfect health), although negative values can be assigned to health states considered to be worse than death. Utility is particularly valuable as a quality weight for length of life. In many decision analyses, cost-effectiveness analyses, and clinical studies, the main outcome is quality-adjusted life years, or QALYs, which are calculated by multiplying length of life by utility. Thus, 10 years in perfect health equal 10 QALYs, while 10 years in a ...